There's been a lot of talk over the years about alternator belts in the Capri. Seems if you have an aftermarket alternator pulley, the rib pattern on the pulley is different enough to eat belts or make them squeal forever. I assume your belt would just bleep a little, mainly on startup or rainy days. The only help I've heard works with aftermarket pulleys is to use a Gates brand belt (industrial rated), go to NAPA and buy NBH257355.
Also, make sure the alternator pulley lines up correctly with the crank pulley, sometimes the alternator bolts bend and rust and the alternator winds up canted at a bit of an angle, and you will NEVER get a belt to stay on...your old belt may have worn in a pattern to keep in it place...peace...Chris